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GENERAL INTRODUCTION
DOWNLOAD A PDF OF OUR MARYLAND SPORTS INJURY CENTER GUIDE TO HEAT AND DEHYDRATION INJURY PREVENTION BY CLICKING HERE!
With all the information available, there are still errors made in
hydration at the Olympic and professional level down to the little league level
of sports. Heat illness is related to the body's ability to adapt and
adjust to an increased core temperature occurring with exertion. If the rate of heat
production or gain exceeds the rate of heat dissipation or loss, then hyperthermia
or high internal body temperature, results.
The two most important methods of heat dissipation are radiation and evaporation.
"Radiation is the transfer of heat to the environment via electromagnetic waves; it
accounts for most heat dissipation. As long as there is a temperature gradient between
the body and the air, 65% of the body's heat is lost by radiation.
Evaporation is the transfer of heat by transformation of perspiration and saliva into
a vapor; it accounts for 30% of the body's heat loss." "When air temperature exceeds
95°F (35°C), radiation of heat from the body ceases and evaporation becomes the only
means of heat loss. Evaporation is maximally efficient in a dry environment. If humidity
reaches 100%, evaporation of sweat is no longer possible and the body loses its ability
to dissipate heat." "Initially, the body attempts to control the core temperature.
A rise in body temperature activates heat receptors in both the hypothalamus and the
periphery, which results in increased shunting of blood to the periphery." When
this mechanism is overwhelmed, problems arise.
Heat Exhaustion and Heat Stroke
Thirst alone is not a good indicator of the need for fluids. Research
demonstrates that exercise in hot adverse conditions can cause dehydration
in as little as 15 minutes. Drinking when in a dehydrated state can
cause gastrointestinal distress. Athletes who say they cannot drink
during a workout because it gives them a stomach ache may be allowing
themselves to become dehydrated before they take their first drink.
Dehydration is cumulative. If lost fluids and minerals go unreplaced
fatigue and heat illness can result. It can manifest as heat cramps,
heat exhaustion and heat stroke.
Heat cramps begin can begin as twitching of the muscles and progress to
localized contractions of the muscles of the legs, arms, or abdomen.
Treatment involves rest and drinking mildly salted fluid.
Heat exhaustion is a form of shock and is the third leading
cause of death among young athletes. It is the inability to continue
exercise in a hot environment and primarily results from sweat loss
and/or inadequate fluid intake. When dehydration (especially greater
than 3% of bodyweight) is superimposed on exercise heat stress, the
cardiovascular system is simply unable to pump sufficient blood to
meet all of the body's needs.
Signs and symptoms can include: profuse
sweating, "heat sensations" on the head/shoulders/chest, weakness,
"rubbery" legs, chills, anxiety, irritability, nausea, vomiting,
muscle cramps, fainting, rapid and weak pulse, pale or flushed skin,
disturbance of vision and incoherence. Treatment consists of rest in
a cool environment, elevation of legs, pouring cool water on the skin
and replacement of fluids orally or intravenously. Recovery is usually
complete within 12 to 48 hours, without further complications. Athletes
suffering from heat exhaustion should not be allowed to practice or
compete for the remainder of that day. Heat exhaustion may be prevented by
proper heat acclimatization; consuming water, electrolytes and
carbohydrates to replace losses; and monitoring ambient conditions
(temperature and humidity) to allow practice sessions to be tailored to
the environment.
Heat stroke is a medical emergency requiring rapid diagnosis and
treatment. It is an elevated core temperature above 104 degrees F
(by rectal thermometer) and altered mental status. Other signs include
hot and dry skin, rapid heart rate, rapid breathing, disorientation,
confusion, combativeness, decreased responsiveness, coma or seizure.
More than half of presenting patients are sweating, especially in cases of
exertional heatstroke.
Heatstroke can occur when the air temperature is as low as 41 degrees F
and often occurs during the early morning. Between 1959 and 1985 there
were 77 heatstroke fatalities at high school and college level.
Heatstroke commonly involves more than one factor: obesity, insufficient
heat acclimatization, dehydration, lack of sleep, fever, drug or alcohol
abuse. Other factors are air temperature, time of day, type of
activity, exercise intensity, exercise duration, and clothing. It
usually occurs among young, motivated males who push their bodies
beyond the point at which they would normally stop exercise if
discipline, competition, or peer pressure were not involved.
Few cases of exercise-induced heatstroke have been reported among
females.
The key to treatment of
heatstroke is rapid cooling. Stopping the activity, removing excess
clothing, getting into the shade, checking the core temperature and
other vital signs and calling 911 must be done immediately. Ice water
immersion or pouring ice water on the person has been described as the
most efficient and rapid method of core temperature cooling. The
majority of patients recover completely within one to six months.
Hyponatremia is a decrease of sodium in the blood and is caused
by over-hydration. Slower runners, 4 1/2 hour plus marathoners, are
affected more frequently; but this is not absolute. Mild cases may be
asymptomatic, but moderate or serious cases may cause elevated BP,
vomiting, altered mental status, bloating, respiratory distress,
seizure or coma. No fluid should be given until urination has begun
and salty foods are encouraged.
For more information on hyponatremia see
Hyponatremia in Athletes
Hydration Guidelines
Thirst alone is not a good indicator of the need for fluids. Research
demonstrates that exercise in hot adverse conditions can cause
dehydration in as little as 15 minutes. It takes at least 7-10 days
to acclimatize to the heat. Loose, light colored clothing should be
worn. No rubberized suits! Weigh yourself before and after training and
replace each pound lost with one pint of fluid. A 1-3% weight loss will
decrease performance.
Pre-event Hydration
Check the
Heat Index Tables to see if it is safe to train or compete.
1. Athletes should consume 50 to 100 ounces of cool fluid above and
beyond their normal intake the day before the event.
2. The athlete should consume 16 to 32 ounces of water 2 hours prior
to the event.
3. Empty your bladder 15 minutes prior to the event.
4. Drink cool water during the event as it is absorbed faster and cools
the body better than warm water.
5. Weigh yourself before the event/practice begins.
During-event Hydration
1. Drink no more than 8-10oz per 15-20 minutes. Do not take any
ephedra products. Sip the water, do not gulp it down.
Post-event Hydration
1. Weight yourself after the event. Replace each pound lost with one pint of water.
2. Sip the water, do not gulp it down.
3. For multi-day events: Weigh yourself before the event and every
morning. If you lose 1%-3% of body weight, re-hydrate by drinking 16oz
per pound lost. If you lose 3%-6%, re-hydrate and back off on your
training intensity the next day. If you are light-headed, fatigue more
easily or sweat profusely, STOP training and do not train the rest of
the day or the next day. If you lose greater than 7%, you must seek
medical attention immediately!
Here is a urine color chart to help you determine your hydration status. Your urine color
should be between #1 and #3 throughout the day.
NCAA GUIDELINES
The NCAA recommends the following guidelines to prevent heat illness: (from the
2008-2009 NCAA SPORTS MEDICINE HANDBOOK)
1. An initial complete medical history
and physical evaluation, followed
by the completion of a yearly
health-status questionnaire
before practice begins, should be
required. A history of previous
heat illness, and the type and duration
of training activities for the
previous month, also are essential.
2. Prevention of heat illness
begins with aerobic conditioning,
which provides partial acclimatization
to the heat. Student-athletes
should gradually increase exposure
to hot and/or humid environmental
conditions over a period of
seven to 10 days to achieve heat
acclimatization. Each exposure
should involve a gradual increase
in the intensity and duration of
exercise until the exercise is comparable
to that likely to occur in
competition. When conditions are
extreme, training or competition
should be held during a cooler
time of day. Hydration should be
maintained during training and
acclimatization.
3. Clothing and protective equipment,
such as helmets, shoulder
pads and shin guards, increase
heat stress by interfering with the
evaporation of sweat and inhibiting
other pathways for heat loss. Darkcolored
clothing increases the
body’s absorption of solar radiation.
Frequent rest periods should
be scheduled so that the gear and
clothing can be loosened to allow
heat loss. During the acclimatization
process, it may be advisable
to use a minimum of protective
gear and clothing and to practice in
T-shirts, shorts, socks and shoes.
Excessive tape and outer clothing
that restrict sweat evaporation
should be avoided. Rubberized
suits should never be used.
4. To identify heat stress conditions,
regular measurements of
environmental conditions are recommended.
Use the ambient temperature
and humidity to assess
heat stress (see Figure 1). Utilize
the wet-bulb temperature, drybulb
temperature and globe temperature
to assess the potential
impact of humidity, air temperature
and solar radiation. A wetbulb
temperature higher than 75
degrees Fahrenheit (24 degrees
Celsius) or humidity above 90 percent
may represent dangerous
conditions, especially if the sun is
shining or the student-athletes are
not acclimatized. A wet-bulb globe
temperature (WBGT) higher than
82 degrees Fahrenheit (28
degrees Celsius) suggests that
careful control of all activity be
undertaken. The value for caution
may need to be adjusted down
when wearing protective equipment
(see reference No. 6).
5. Dehydration must be avoided
not only because it hinders performance,
but also because it can
result in profound heat illness.
Fluid replacement must be readily
available. Student-athletes should
be encouraged to drink as much
and as frequently as comfort
allows. They should drink one to
two cups of water in the hour
before practice or competition,
and continue drinking during activity
(every 15 to 20 minutes). For
activity up to two hours in duration,
most weight loss represents
water loss, and that fluid loss
should be replaced as soon as
possible. After activity, the student-
athlete should rehydrate with
a volume that exceeds the amount
lost during the activity. A twopound
weight loss represents
approximately one quart of fluid
loss. Urine volume and color can
be used to assess general hydration.
If output is plentiful and the
color is “pale yellow or straw-colored,”
the student-athlete is not
dehydrated.
Water and carbohydrate/electrolyte
drinks are appropriate for
exercise in heat. Carbohydrate/
electrolyte drinks enhance fluid
intake, and the electrolytes aid in
the retention of fluid. In addition,
the carbohydrates provide energy
and help maintain immune and
cognitive function.
6. By recording the body weight of
each student-athlete before and
after workout or practice, progressive
dehydration or loss of body
fluids can be detected, and the
potential harmful effects of dehydration
can be avoided. Those who
lose five percent of their body
weight or more over a period of
several days should be evaluated
medically and their activity restricted
until rehydration has occurred.
7. Some student-athletes may be
more susceptible to heat illness.
Susceptible individuals include
those with: inadequate acclimatization
or aerobic fitness, excess
body fat, a history of heat illness, a
febrile condition, inadequate rehydration,
and those who regularly
push themselves to capacity. Also,
substances with a diuretic effect or
that act as stimulants may
increase risk of heat illness. These
substances may be found in some
prescription and over-the-counter
drugs, nutritional supplements
and foods.
Student-athletes should be
informed of and monitored for
signs of heat illness such as: cessation
of sweating, weakness,
cramping, rapid and weak pulse,
pale or flushed skin, excessive
fatigue, nausea, unsteadiness, disturbance
of vision and incoherency.
If heat illness is suspected,
prompt emergency treatment
is recommended. When training
in hot and/or humid conditions,
student-athletes should train with
a partner or be under observation
by a coach or athletic trainer.
NATA Consensus Statement Recommendations
The consensus statement lists seven key recommendations for a 14-day heat-acclimatization period prior to full-scale athletic participation by secondary school students, as follows:
1. During the first five days of the heat-acclimatization process, athletes may not participate in more than one practice per day.
2. If a practice is interrupted by inclement weather or heat restrictions, the practice should recommence once conditions are deemed safe, but total practice time should not exceed three hours per day.
3. A one-hour maximum walk-through is permitted during the first five days of the heat-acclimatization period; however, a three-hour recovery period should be inserted between the practice and walk-through (or vice versa).
4. During the first two days of the heat-acclimatization period, in sports requiring helmets or shoulder pads, a helmet should be the only protective equipment permitted (goalies, as in the case of field hockey and related sports, should not wear full protective gear or perform activities that would require protective equipment). During days three through five, only helmets and shoulder pads should be worn. Beginning on day six, all protective equipment may be worn and full contact may begin.
5. Beginning no earlier than the sixth day and continuing through the 14th day, double-practice days must be followed by a single-practice day. On single-practice days, one walk-through is permitted, but it must be separated from the practice by at least three hours of continuous rest. When a double-practice day is followed by a rest day, another double-practice day is permitted after the rest day.
6. On a double-practice day, neither practice’s duration should exceed three hours total, and student-athletes should not participate in more than five total hours of practice. Warm-up, stretching, cool-down, walkthrough, conditioning and weight-room activities are included as part of the practice time. The two practices should be separated by at least three continuous hours in a cool environment.
7. Because the risk of exertional heat illnesses during the pre-season heat-acclimatization period is high, the consensus statement strongly recommends that an athletic trainer be on site before, during, and after all practices.
See
Momsteam: Fluid Guidelines for Young Athletes
2003 USA TRACK AND FIELD GUIDELINES
It is recommended that long distance runners consume 1 liter of fluid
for every liter lost during a race. For any race longer than one hour,
the following procedure is suggested to determine individual fluid needs:
1. Be properly hydrated BEFORE the workout, i.e. your urine should be
very slightly yellow or clear.
2. Do a warm-up to the point of lightly perspiring and urinate if
necessary.
3. Weigh yourself naked.
4. Run for one hour at race intensity.
5. Drink a MEASURED amount of fluid of your choice during the
workout.
6. Do not urinate during the workout.
7. After the workout weigh yourself immediately on the same scale.
8. Urinate and/or drink as necessary.
Use the following formula to calculate your hydration requirements:
Pre-workout body weight (kg) from Step 3: _____ kg
(To convert from pounds to kilograms, divide pounds by 2.2)
Post-workout body weight (kg) from Step 7: _____ kg
........................................................... = _____ kg
of body weight lost during the workout.
.................................. _____ kg x 1000 = ______ grams of body
weight lost during the workout
Grams of body weight lost + fluid (ml) consumed from Step 5 = _____ ml
The above ml of fluid is the ml of fluid per hour needed to
properly hydrate.
To convert oz to ml: oz x 30 = ml.
To convert ml to oz: ml/30 = oz.
CARBOHYDRATE BEVERAGES
Carbohydrates consumed immediately after and two hours after exercise
can enhance muscle glycogen restoration.(12) Most oral rehydration
solution contain less than 6% carbohydrates (about 55 calories per 8oz.)
because research has shown that the greatest rates of fluid absorption
are usually stimulated by solution containing from 2-6% carbohydrates.
Increasing carbohydrate content beyond 6% often reduces the rate of fluid
absorption.(20) Research shows the 6% carbohydrate concentration is
absorbed at least 30% faster than water. Higher glucose levels are
maintained with ingestion of this type of beverage.(9)
Gatorade (6% carbohydrate/electrolyte solution) was absorbed
significantly faster than water during both exercise and recovery
periods. Exercise did not influence the absorption process.(11)
Exercise performance improved significantly with carbohydrate
feedings. This study recommends ingesting 30-60g/hour of
carbohydrate during exercise to improve performance.(13)
Solutions with multiple transportable substrates that can stimulate
several different solute transport mechanisms produce greater solute
and water absorption than solutions with only a single transport
medium. The 6% CHO solution containing a combination of free glucose
and fructose are suggested for maximizing waster and CHO
absorption.(18)
To calculate the carbohydrate percentage of any beverage:
Divide the number of grams of carbohydrate per serving (in milliliters)
and multiply by 100, e.g. 14 grams per 8oz. (1oz.x30=milliliters)
14/240 mlx100= 5.83 or 6%
ELECTOLYTES
Potassium 30mg/8oz
Sodium 110 mg/8oz
FRUCTOSE BEVERAGES
When the subjects ingested the beverage every 20 minutes during two hours of exercise, the fructose beverage was not as readily available for energy as the glucose-containing beverages. The glucose polymer did not provide any metabolic advantage over the glucose-free beverage.(14) Consumption of fructose was associated with greater incidence of gastrointestinal distress due to its slow absorption rate, a greater loss of plasma volume, greater stress hormone response and substantially poor exercise performance.(17)
CARBONATED BEVERAGES
Carbonated soft drinks contain carbohydrates in a concentration of 10-11%. Compared to the typical sport drinks, such beverages are absorbed slowly. In addition, the carbonation turns into carbon dioxide gas when warmed in the stomach and can cause gastrointestinal distress. The caffeine found in many soft drinks actually increased fluid lost by stimulating urine production.(19)
SUPER ORAL REHYDRATION
A new concept of super oral rehydration has been proposed in which nutrients other than carbohydrates are also included in the beverage like amino acids. The theory needs to be confirmed.(20)
VOLUME OF FLUID INGESTED
The volume of fluid ingested is a powerful regulator of gastric emptying. There was greater gastric emptying with rehydration of 150% of fluid lost. However, this was attained via relatively large gastric fluid volume, with concomitantly large urine volumes. Thus, forced intake of a relatively dilute solution is not an effective method of rapid rehydration and may be detrimental to subsequent performance.(16)
EXERTIONAL HEAT ILLNESS
Recruits at higher risk for developing EHI (exertional heat illness) had a BMI of >22/kg/mm and 1.5 mile run time of >12 minutes. These recruits had an eightfold higher risk for developing EHI during basic training when compared to those with BMI <22 and a 1.5 mile run time of <10 minutes. Only 1/5 of male recruits met these criteria for high risk, but they accounted for nearly half of the EHI cases occurring during the 12 weeks basic training course.(10)
CHILDREN
Studies have shown that the main maturational differences to exercise in the heat (mostly sweating rate and composition) occur at late puberty and adulthood, rather than from pre- to mid-puberty.(15)
WHEELCHAIR
Individuals with spinal cord injury possess limited
autonomic control of heat dissipation (sweat gland
secretion, redistribution of cardiac output, vasodilation
in cutaneous vessels) below the level of injury. The
magnitude of their thermoregulatory impairment is related
to the level and completeness of the spinal cord lesion.
Other factors are impaired sympathetic cardiac stimulation
which results in lower stroke volume and cardiac output and
decreased venous return to the heart than that of able-bodied
individuals; reduced thermoregulatory response for a given
core temperature; unique movements of upper-body wheelchair
propulsion, when compared to lower body exercise of equal
intensity, produce enhanced strain, evidenced by greater
plasma volume loss and catecholamine concentrations;
medications (oxybutynin and phenoxybenzamine for bladder
control) may negatively affect sweating and
thermoregulation.(8)
What We Can Learn From the Korey Stringer Episode
1. A doctor and ambulance should be on the field.
There was no doctor nor an ambulance on the field for Kory Stringer.
2. Listen to weather warnings. The heat index on the day Stringer died was 109!
See
See
Heat Index Table
Don't practice in full pads and wear light colored jerseys!
Have a shaded area to go to when not in a play.
Have ice available and make use of it (head and neck).
Have mist sprayers available.
3. Pay attention to the players. Less shouting at players, more encouragement.
4. Come to practice in shape - get in shape during the off season.
5. Stringer vomited 5 times on the first day of practice - this is
a good clue that the player is not in shape and is not heat acclimated!
6. If you continue to sweat profusely after practice and the remainder
of that day and night - don't practice the next day.
7. Weight the players before and after practice. Stringer lost 6 lbs
the first day of practice.
8. Call 911 immediately. Why was Stringer in the trailer for 45 minutes and not on his way
to the hospital immediately?
9. Why was a 22 year old trainer attending to multi-million dollar
professional football players?
10. Why wasn't Stringer's temperature taken (the trainer did not even
have a thermometer in the trailer)? If he was "unresponsive"
what took so long to get him to the hospital!
For more information see
Heat Illness Prevention Tips
National Federation of High School Sports: Heat Stress and Athletic Participation
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HEAT INJURIES AND HYDRATION GUIDELINES